This study aimed to examine the relationship between lower limb muscle mass in pregnant women and factors affecting it, such as physical activity, weight gain during pregnancy, and body mass index (BMI) prior to pregnancy. Subjects and Methods Five hundred and twenty pregnant women were asked to answer a self-administered questionnaire, which included questions regarding their prior to pregnant weight, height, and level of physical activity. Their weight and lower limb muscle mass were measured

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... using a body composition analyzer (InBody270). Physical activity pertained to the presence or absence of exercise habits and daily activity levels (NEAT questionnaire). A t-test was performed separately for each of the primipara and multipara groups, and multiple regression analysis was performed to examine the relationship between lower limb muscle mass and factors associated with it. Results A total of 484 respondents (229 primiparas and 255 multiparas, aged 18-44 years at 5-40 weeks of gestation) with an average lower limb muscle mass of 11.53±1.68kg were included in this study. The muscle mass of both primiparas and multiparas was significantly higher in the high group (primiparas: 11.76±1.49kg and multiparas: 12.41± 1.72kg) than in the low group (10.97±1.70kg and 11.24±1.63kg). BMI at non-pregnancy was significantly higher in the high group (11.98±1.60kg and 12.17±1.56kg) than in the low group (10.71±1.60kg and 11.46±1.85kg). Among primiparas, lower limb muscle mass was associated with factors, such as prior to pregnant BMI and weight gain and prepregnancy exercise habits (β=0.339, 0.227, 0.136, respectively), with a contribution ratio of 18.8%. Among multiparas, lower limb muscle mass was associated with, weight gain, prior to pregnant BMI and daily activity levels (β=0.258, 0.245, 0.169, respectively), with a contribution ratio of 15.6%. Among pregnant women who had normal BMI prior to pregnancy, the lower limb muscle mass was higher in women with weight gain ranging from 4.9kg to >8.5kg at 16-27 weeks and 28-37 weeks of gestation than in those who did not experience weight gain. Conclusion Prior to pregnant BMI and weight gain affected the muscle mass of the lower limbs of pregnant women. Prepregnancy exercise habit affected the lower limb muscle mass of primiparas, while the level of daily activity affected the lower limb muscle mass of multiparas.